Add lot_prefix to products; compose LOT number from prefix + date suffix

Products now have a configurable lot_prefix (e.g. "112"). In the batch form
the prefix is shown read-only next to the suffix input (JJMMTT), and the full
lot_number (e.g. "112-260912") is composed automatically and stored.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Filament/User/Resources/ProductResource/RelationManagers/BatchesRelationManager.php

@@ -24,11 +24,31 @@ class BatchesRelationManager extends RelationManager
     public function form(Form $form): Form
     {
         return $form->schema([
-            Forms\Components\TextInput::make('lot_number')
+            Forms\Components\TextInput::make('lot_suffix')
                 ->label('LOT-Nummer')
+                ->prefix(fn ($livewire): ?string => $livewire->getOwnerRecord()->lot_prefix
+                    ? $livewire->getOwnerRecord()->lot_prefix . ' -'
+                    : null
+                )
+                ->placeholder('JJMMTT')
+                ->maxLength(50)
                 ->required()
-                ->unique(ignoreRecord: true)
-                ->maxLength(255),
+                ->dehydrated(false)
+                ->live()
+                ->afterStateHydrated(function ($component, $record) {
+                    if (! $record?->lot_number) return;
+                    $pos = strrpos($record->lot_number, '-');
+                    $component->state($pos !== false
+                        ? substr($record->lot_number, $pos + 1)
+                        : $record->lot_number
+                    );
+                })
+                ->afterStateUpdated(function ($state, $set, $livewire) {
+                    $prefix = $livewire->getOwnerRecord()->lot_prefix;
+                    $set('lot_number', $prefix ? "{$prefix}-{$state}" : $state);
+                }),
+
+            Forms\Components\Hidden::make('lot_number'),
 
             Forms\Components\Select::make('size_id')
                 ->label('Variante (Verpackung)')